1. Field of the Invention
The present invention relates to a circuit board including a first portion relatively resistant to deformation and a second portion more flexible and less resistant to deformation than the first portion, and also relates to a method for producing the same.
2. Description of the Related Art
An example of a conventional circuit board of this type is described in International Publication No. WO 2011/040393. In International Publication No. WO 2011/040393, the circuit board includes a main portion obtained by stacking base sheets made of a flexible material (e.g., polyimide or liquid crystal polymer). The main portion includes a first portion relatively resistant to deformation and a second portion more flexible and less resistant to deformation than the first portion. The main portion has provided therein wiring conductors for electrically connecting an electronic component and various electrodes and reinforcing insulation films made of a more rigid material (e.g., epoxy resin) than the base sheets. The first portion is formed by providing the reinforcing insulation films so as to, when viewed in a plan view in the stacking direction of the base sheets, cover areas where the base sheets are not desired to be deformed.
The above conventional circuit board uses the reinforcing insulation films to form the first portion. However, if the reinforcing insulation films increase in area, the characteristics of the main portion greatly depend on the reinforcing insulation films, and therefore, the characteristics of the base sheets (such as low relative permittivity, low loss, and low water absorption) cannot be fully utilized. Moreover, the reinforcing insulation films are relatively large in area, and do not stick to the base sheets well, so that the bonding strength between the sheets might be insufficient.